According to Wikipedia’s article on Video Game Development Parties, a third-party game developer is a game developer that is not part of any particular first party console developer. Notable third-party companies include Electronic Arts, Activision, and Ubisoft.
Examples of usage:
· “Third-party developers make some awesome games, but I’ve been looking forward to first-party titles, recently.”
· “The third-party developers had quite the showing at this year’s E3.”
References: http://en.wikipedia.org/wiki/Video_game_development_party. Retrieved on 6/25/2012.